In situ synthesis of ZIF-67 as sacrificial template within the sublayer of forward osmosis membrane to minimize...

Internal concentration polarization (ICP) in the support layer significantly decreases the water flux performance of forward osmosis (FO) membranes. To overcome this, we developed a novel method for creating a highly porous support layer using ZIF-67 nanoparticles as a sacrificial template. The ZIF-67 nanoparticles were synthesized in a polymer casting solution at different precursor concentrations, including Co²⁺ and 2-methylimidazole. This method enhances nanoparticle dispersion in the support layer and enables scalable membrane fabrication. ZIF-67 nanoparticles are incorporated into the support layer matrix during phase inversion, then removed by immersing the ZIF-67-incorporated support layer in water, yielding a porous support layer. The modified support layer exhibited a porosity of 83%, which is 15% higher than that of the unmodified membrane, attributed to the templating effect of ZIF-67 nanoparticles. The performance of TFC-FO membranes was evaluated in a FO setup to correlate improved support layer characteristics with FO separation performance. The TFC-2 membrane (fabricated with 3.0 wt.% ZIF-67 precursors) exhibited water fluxes of 29.5 LMH (in FO mode) and 56.4 LMH (in PRO mode), representing a 2.3-fold increase compared to that of the control TFC membrane (13.2/24.6 LMH in FO/PRO modes, respectively). Additionally, the structural parameter decreased from 593 µm in TFC to 242 µm in TFC-2 membranes, indicating a substantial reduction in ICP. These results demonstrate that the in-situ synthesis of ZIF-67 as a sacrificial template is a simple and effective strategy for preparing high-porosity support layers with reduced ICP.